The present invention relates to lung surfactant compositions which are capable of forming a dynamic swelling phase when dispersed in a medium containing electrolytes. The dynamic swelling process can be observed by polarising microscopy and results in formation of a birefringent network or tubules at an air/liquid interface. The dynamic swelling process results in a spreading of the lung surfactant over an increased surface area compared to the spreading of the lung surfactant in a non-dynamic swelling phase. The spreading takes place during a specific span of time after dispersion of a lung surfactant in e.g. a physiological electrolyte solution. Hereby, a more active spreading of the lung surfactant into the alveoli can be obtained after administration to the lungs, which in turn opens the possibility to use such a composition as a carrier for therapeutically, prophylactically and/or diagnostically active substances into the lungs or other organs or body areas that are hard to access.
The invention also relates to a pharmaceutical composition and a pharmaceutical kit comprising a lung surfactant composition as well as to a method for the treatment, prevention and/or diagnose of respiratory distress syndrome (IRDS or ARDS) or other pulmonary diseases that are associated with a deficiency of a lung surfactant.
Lung surfactants (LS) are complex and highly surface-active materials composed of lipids and proteins that are found in the fluid lining the alveolar surface of the lungs. Their principal property is to reduce the surface tension in the lungs, which is achieved through the presence of the lipids as an organised structure at the air-liquid interface in the alveoli. LS prevents alveolar collapse at low lung volumes and decreases the work of breathing during normal and forced respiration (biophysical functions). In addition, it is involved in the protection of the lungs from injuries and infections caused by inhaled particles and microorganisms (immunological, non-biophysical functions). LS is synthesised and secreted by alveolar type II cells. (For a review, see Robertson and Taeusch, 1995.)
The constitution of a lung surfactant may vary with various factors such as species, age, and general health conditions of the subject. Various natural and synthetic constituents can substitute for each other in a surfactant. Therefore, even a non-rigorous definition of what the lung surfactant is and what should be included in a lung surfactant for therapeutic use is dependent on the situation. Surfactants isolated from lung lavage of healthy mammals contain about 10% protein (half of which is surfactant specific), and about 90% lipids, of which about 80% are phospholipids and about 20% are neutral lipids, including about 10% unesterified cholesterol. The phospholipid fraction contains mostly (about 76%) phosphatidylcholine (PC), about two thirds is dipalmitoyl phosphatidylcholine (DPPC), and the rest is unsaturated. About 11% of the phospholipids are made up of phosphatidylglycerol (PG), about 4% phosphatidylinositol, about 3% phosphatidylethanolamine, about 2% phosphatidylserine, about 1.5% sphingomyelin and about 0.2% lysophosphatidylcholine. Surfactant protein A (SP-A) represents 4% of surfactant and SP-B and SP-C and SP-D each make up less than 1%, according to current estimates.
SP-A and SP-D belong to the collectin subgroup of the G-type lectin superfamily. SP-A binds dipalmitoyl phosphatidylcholine and SP-D binds phosphatidylinositol. SP-A also interacts with alveolar type II cells, implicating SP-A in surfactant phospholipid homeostasis. SP-A is required for the formation of tubular myelin from secreted lamellar body material.
Surfactant deficiency remains the most common and serious pulmonary affliction of premature infants. Surfactant deficiency is the major factor responsible for respiratory distress syndrome of the newborn (IRDS) and for adult respiratory distress syndrome (ARDS). Since the 1960xe2x80x2s, the exogenous administration of lung surfactant for the treatment of these syndromes has been studied.
A pathophysiologic role for surfactant was first appreciated in premature infants with respiratory distress syndrome (IRDS) and hyaline membrane disease Use of exogenous lung surfactant and corticosteroid administration has made a major impact on improving survival and reducing morbidity in this disease with consequent alterations in the clinical and radiographic course.
Initial attempts at improving the treatment of RDS with lung surfactant replacement during the 1960xe2x80x2s (Chu et al., 1967) failed, largely because of a lack of knowledge about lung surfactant compositions and distributions. Liggins and colleagues (Liggins et al., 1972) were the first to utilise corticosteroids for the enhancement of foetal lung maturation, thereby reducing the risks and complications of RDS after birth. It is feasible that combining corticosteroids with thyroid-releasing hormone will enhance prenatal prophylaxis for RDS, and also inositol can be given as a substrate for lung surfactant production to infants in the early course of RDS.
A number of approaches for the design and the use of lung surfactant replacement for RDS have also been tried. The most straightforward approach is to replace with human lung surfactant. Human pulmonary lung surfactant can only be harvested by lavage procedures, though, which may disrupt its preexisting biophysical and biochemical microorganisation. As seen in a study by Hallman and co-workers, (Hallman et al., 1983), such a preparation was successful in clinical trials, but because of the difficulties in obtaining large quantities of human lung surfactant, it is not in commercial production.
These limitations make the production of synthetic lung surfactant desirable A second approach is therefore to learn the functions of the various lung surfactant constituents and then construct lung surfactants that might be more easily obtained or less expensive than the isolation of the natural products.
Exosurf is a commercially available preparation containing DPPC, hexadecanol and tyloxapol. Hexadecanol and tyloxapol mimic, to some degree, the functions of surfactant proteins, PG and other lipids in natural lung surfactant. Several groups have added surfactant proteins to lipids, designing the proteins to mimic structure and function of native surfactant proteins.
Furthermore, there are new strategies that add surfactant proteins to lipid mixtures that include formulating proteins using de novo peptide synthesis or recombinant DNA techniques (Yao et al., 1990)
An ideal therapeutic lung surfactant should share many of the attributes of any ideal therapy. It should be stable, readily available, easy to make, inexpensive and have an easy route of administration, a half-life consonant with the disease process, and fully understood mechanisms of action, metabolism and catabolism. It should have maximum efficacy for the disease without toxicity, intolerance, immunogenicity or side effects. It should mimic the effects of the natural lung surfactant, improve the gas exchange in the lungs, improve lung mechanics, improve functional residual capacity, resist inactivation, display optimal distribution characteristics, and have a known clearance mechanism. Its use should completely reverse the primary disease process and repair or allow the body to repair secondary damage from the primary disease.
Available therapeutic lung surfactants are of two types: those that are prepared from mammalian lungs and those made from synthetic compounds. Bovine and porcine surfactants contain SP-8 and SP-C, associated with phospholipids, but SP-A and SP-D are only present in the whole natural surfactant. Examples of synthetic lung surfactants that are commercially available at present are Exosurf and ALEC.
The commercially available lung surfactants are mostly presented as ready-mixed liquids, but Exosurf and Alveofact are supplied as a lyophilised powder that has to be reconstituted with saline before use.
Surfactant therapy is at present an established part of routine clinical management of newborn infants with IRDS. An initial dose of about 100 mg/kg is usually needed to compensate for the deficiency of alveolar surfactant (lung surfactant) in these babies, and repeated treatment is required in many cases. Recent experimental and clinical data indicate that large doses of exogenous lung surfactant may be beneficial also in conditions characterised by inactivation of lung surfactant, caused by, for example, aspiration of meconium, infection, or disturbed alveolar permeability with leakage of plasma proteins into air spaces.
The acute response to lung surfactant therapy depends on the quality of the exogenous material (modified natural lung surfactant is generally more effective than protein-free synthetic surfactants), timing of treatment in relation to the clinical course (treatment at an early state of the disease is better than later treatment and may reduce the subsequent need for mechanical ventilation) and mode of delivery (rapid instillation via a tracheal tube leads to a more uniform distribution and is more effective than slow airway infusion). Treatment with aerosolised surfactant improves lung function in animal models of surfactant deficiency, but is usually associated with large loss of the nebulised material in the delivery system. Furthermore, data from experiments on immature newborn lambs indicate that treatment response may depend on the mode of resuscitation at birth, and that manual ventilation with just a few large breaths may compromise the effect of subsequent surfactant therapy. The widespread clinical use of lung surfactant has reduced neonatal mortality and lowered costs for intensive care in developed countries.
The most efficient lung surfactants at present are prepared from mammalian lungs. The yield is very low and the therapy is therefore very expensive. Therefore there is an urgent need to improve their efficiency and to standardise their application.
The present invention provides a lung surfactant composition comprising a lung surfactant, whichxe2x80x94when dispersed as powder or particles in 0.9% w/w sodium chloride in a concentration of 10% w/w at ambient temperaturexe2x80x94is capable of forming, in the course of swelling, a birefringent network or tubules at an air-liquid-solid interface within a time period of from about 0.5 to abut 120 min such as, e.g. from about 3 to about 60 min as observed by polarising microscopy.
The birefringent network or tubules are formed during a dynamic swelling process that takes place in the span of time from the lung surfactant is dispersed in a medium containing electrolytes and to the steady-state of swelling is reached (i.e. at equilibrium).
Thus, in another aspect the invention relates to a lung surfactant composition, whichxe2x80x94when dispersed as a powder or as particles in an electrolyte solution having an ionic strength of at least about 5 mM such as, e.g., at least about 10 mM, at least about 15 mM, at least about 20 mM, at least about 25 mM, at least about 50 mM, at least about 75 mM, at least about 100 mM or at least about 125 mM or at an ionic strength corresponding to physiological conditions, and the thus obtained dispersion has a concentration of water of at least about 55% w/w such as, e.g. at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95% or at least about 98% w/w,xe2x80x94is subject to a dynamic swelling process during which a birefringent network or tubules are formed, as observed by polarising microscopy, and the dynamic swelling process ends when steady-state is reached.
When dispersed in an electrolyte solution a liquid crystalline lamellar phase of the phospholipids is formed. The lipid-protein bilayer structure has been found to be organising towards an active establishment of an equilibrium composition, which is microscopically perceptible as a formation of a birefringent complex network. A LS composition for administration e.g. at a predetermined time point or during a well-defined time period is provided as well as means for determining said optimal time point or time period for a lung surfactant composition.
A more active spreading of a lung surfactant into the alveoli can be obtained when applying to the lungs or other parts of the respiratory system a lung surfactant that has dynamic swelling behaviour in a medium containing electrolytes. In this manner an improved treatment, prevention or diagnosis can be obtained.
Furthermore, a lung surfactant composition according to the invention may be used as a carrier for therapeutically, prophylactically and/or diagnostically active substances e.g. for pulmonary drug delivery.
The invention also provides a pharmaceutical composition, a pharmaceutical kit and method for an improved treatment of respiratory distress syndrome (RDS) or other respiratory or pulmonary diseases that may be associated with deficiency of surfactant.
In a still further aspect the invention provides an in vitro validation method for testing individual batches of a lung surfactant composition which has dynamic swelling behaviour when dispersed in an electrolyte solution, the method comprising
a) determining txc2xd for maximum dynamic swelling as described herein,
b) comparing the thus obtained txc2xd with a in vivoxe2x80x94in vitro correlation curve, obtained as described herein, and
c) evaluating the batch as acceptable or not acceptable.
The invention also relates to an in vitro method for evaluating the therapeutic, prophylactic and/or diagnostic effect of a lung surfactant composition, which has dynamic swelling behaviour when dispersed in an electrolyte solution, the method comprising determining the half-life of the steady-state swelling and comparing the thus obtained half-life with in vivo-in vitro correlation curves in order to predict the therapeutic, prophylactic and/or diagnostic effect.